page_title: Sound level meter
section_title: LAT or Leq: Equivalent continuous sound level
hierarchical_section_title: Sound level meter / Measurements / LAT or Leq: Equivalent continuous sound level
caption_attribution_description: English: Graph of a continuous LAeq sound level measurement
context_page_description: A sound level meter is used for acoustic measurements. It is commonly a hand-held instrument with a microphone. The best type of microphone for sound level meters is the condenser microphone, which combines precision with stability and reliability. The diaphragm of the microphone responds to changes in air pressure caused by sound waves. That is why the instrument is sometimes referred to as a Sound Pressure Level Meter. This movement of the diaphragm, i.e. the sound pressure deviation, is converted into an electrical signal. While describing sound in terms of sound pressure is possible, a logarithmic conversion is usually applied and the sound pressure level is stated instead, with 0 dB SPL equal to 20 micropascals.
  A microphone is distinguishable by the voltage value produced when a known, constant sound pressure is applied. This is known as the microphone sensitivity. The instrument needs to know the sensitivity of the particular microphone being used. Using this information, the instrument is able to accurately convert the electrical signal back to a sound pressure, and display the resulting sound pressure level.
context_section_description: eq = equivalent. Equivalent values are a form of time weighting that is easier to read on a display than the instantaneous sound level.
  If you look at these graphs of sound level over time, the area under the blue curve represents the energy. The horizontal red line drawn to represent the same area under the blue curve, gives us the LAeq. That is the equivalent value or average of the energy over the entire graph.
  LAeq is not always a straight line. If the LAeq is plotted as the equivalent from the beginning of the graph to each of the measurement points, the plot is shown in the second graph.
  Sound exposure level—in decibels—is not much used in industrial noise measurement. Instead, the time-averaged value is used. This is the time average sound level or as it is usually called the 'equivalent continuous sound level' has the formal symbol LAT as described in paragraph 3,9 "Definitions" of IEC 61672-1 where many correct formal symbols and their common abbreviations are given. These mainly follow the formal ISO acoustic definitions. However, for mainly historical reasons, LAT is commonly referred to as  Leq.
  Formally, LAT is 10 times the base 10 logarithm of the ratio of a root-mean-square A-weighted sound pressure during a stated time interval to the reference sound pressure and there is no time constant involved. To measure LAT an integrating-averaging meter is needed; this in concept takes the sound exposure, divides it by time and then takes the logarithm of the result.
caption: Graph of a continuous LAeq sound level measurement
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